Inferior vena cava filter with stability features

ABSTRACT

A filter having a first set of members and a second set of members defining a trap sized to fit into a blood vessel. Each of the first and second members are configured to resiliently extend from the trap. At least one of the first set of members includes a first surface for engaging the vessel wall such that the at least one of the first set of members resists downstream movement within the vessel. At least one of the second set of members includes a second surface for engaging the vessel wall such that the at least one second member resists upstream movement within the vessel.

PRIORITY DATA AND INCORPORATION BY REFERENCE

This application claims the benefit of priority to U.S. ProvisionalPatent Application No. 60/870,722 filed Dec. 19, 2006, which isincorporated by reference in its entirety.

TECHNICAL FIELD

The invention relates to a filter device that can be placed via acatheter delivery system in a vessel of a mammalian body to reduce therisk of embolisms. If needed, such filter can be removed from the vesselof a mammalian body without causing traumatic damage to the vessel of amammalian body. The invention further relates to features thatfacilitate retrieval and prevent migration of the filter.

BACKGROUND ART

Inferior vena cava filters, also called IVC filters or Greenfieldfilters, are medical devices that are implanted into the inferior venacava to prevent pulmonary emboli. They work by trapping emboli whilestill permitting the flow of blood, thereby preventing an embolus fromsealing off a vessel. IVC filters are used if anticoagulation isineffective or contraindicated.

IVC filters are inserted via the blood vessels (i.e., placedendovascularly). Known filters can be compressed into thin catheterspermitting access to the venous system via the femoral vein or theinternal jugular vein. A catheter is guided into the IVC usingfluoroscopic guidance. The filter is pushed through the catheter anddeployed into the desired location. IVC filters are usually positionedjust below the junction of the IVC and the lowest renal vein.

IVC filters may be permanent or retrievable. Retrievable filters have aconfiguration that allows them to be pulled back into a catheter orsheath to be removed. In either case, these filters also includestructure to anchor the filter in place within the vena cava. Typicalfeatures include elongate diverging anchor elements called secondextension elements. These frequently have hooked ends that penetrate thevessel wall to prevent migration within and along the vessel. Some typesof filters also have first extension elements which contact the wall ofthe vessel at a point that is axially displaced from the point ofcontact by the second extension elements. This apposition helps to keepthe filter axially oriented (i.e., prevents tipping) and centered.

U.S. Pat. No. 4,494,531 to Gianturco describes a filter with multiplestrands of shape memory wire which are interconnected and waddedtogether to form a mesh. The filter has projections at either end of themesh that anchor it within the inferior vena cava. Each anchor has awire loop act as a stop to prevent the anchors from penetrating toodeeply.

U.S. Pat. Nos. 4,643,184 and 4,272,823 to Mobin-Uddin describe a filterwith a central cylindrical column which interconnects a pair of corollasof elongate hoops forming two tiers of metal wire. The hoops are eachinclined outwardly from the column. Each of loops is formed of two wireswith the outer ends of the wires being bent toward each other to formshort circumferentially extending portions and then 180° in the sameplane to form oppositely extending circumferential portions. The extremeends of the wires are bent radially outwardly into hooks. The wires ofeach loop may be joined at the crowns of the open loops to cause them tohook together. The circumferentially bent portions at the ends of thehoops form stops or barriers which prevents the hooks at the ends frompenetrating the wall of the passageway (artery) sufficient to prevent apuncture.

U.S. Pat. No. 5,755,790 to Chevillon, et al. describes a filter with acentral portion and two corollas connected by the central portion. Theupstream corolla has spines with flat shoes at their ends that contactthe arterial wall. The support corolla has folded elongate hoops thatterminate in v-shaped portion that also contacts the arterial walldownstream of the upstream shoes. The device is removable and does notpenetrate the arterial wall.

U.S. Pat. Nos. 6,007,558, 6,258,026, and Publication No. 2005/0234503 toRavenscroft, et al. describe a filter with first and second corollasjoined at the downstream end like the ribs of an umbrella but with oneset of ribs forming the downstream corolla and one set forming theupstream corolla. The upstream corolla ribs have hooks at their ends.The downstream corolla rib ends are turned toward the axial center offilter, thereby preventing the ends from projecting into the arterialwalls.

U.S. Pat. Nos. 6,231,589 and 6,706,054 to Wessman, et al. describe afilter with first and second corollas connected by a central cylindricalmember forming two corollas each with ribs extending radially andupstream. The upstream corolla ribs and downstream ribs have similarstructures which bifurcate toward their ends. Barbs are located at thepoints where the upstream ribs bifurcate to anchor the filter in theartery.

U.S. Pat. No. 6,972,025 to WasDyke describes a filter with first andsecond corollas joined at the downstream end like the ribs of anumbrella but with one set of ribs forming the downstream corolla and oneset forming the upstream corolla. The upstream corolla ribs have hooksat their ends. The downstream corolla rib ends are rounded and made ofbioabsorbable material.

U.S. Pat. No. 7,037,320 to Brady, et al. describes a filter with asupport which has round wires the form hoops. The hoop formed by thewires ensures that in the expanded position, a filter body will besupported by the support frame in apposition with the interior wall ofthe blood vessel. The wires have a strain distributing loop that allowsthe diameter of the hoop to self-adjust to the blood vessel size. Thestrain relieving loop enhances the compliance of bend points in thecircumferential seal of the hoop against the vessel wall.

US Patent Publication No. 2005/0045183 describes a filter with a corollawith extensions having wall-penetrating hook or barb. The extensionsform a single array at a single longitudinal location, like the spokesof an umbrella or the legs of a spider.

US Patent Publication Nos. 2006/0030875 and 2006/0106417 to Tessmerdescribe a filter with first and second corollas joined at thedownstream end like the ribs of an umbrella but with one set of ribsforming the downstream corolla and one set forming the upstream corolla.The upstream corolla ribs have hooks at their ends. The downstreamcorolla rib ends are turned toward the axial center of filter, therebypreventing the ends from projecting into the arterial walls.

US Patent Publication No. 2006/0178695 to Decant, et al, shows a filterwith a corolla with extensions having wall-penetrating hook or barb. Theextensions form a single array at a single longitudinal location.

U.S. Pat. Nos. 5,669,933 and 5,836,968 to Simon show a filter with abasket and extensions that curve toward the downstream end of thechannel.

U.S. Pat. No. 6,468,290 to Weldon, et al, shows a filter with an arrayof extensions that have hooks that curve toward the downstreamdirection.

There are a number of conflicting issues concerning the design of venacava filters. Filters that are intended to be removed must hold theirposition in the vena cava but in a manner that does not cause unduedamage to the vena cava wall. Also, the design features that hold thefilter in place must also not promote tissue growth that would make itdifficult to remove the filter atraumatically. The filter may need to beself-orienting to some extent as well so there may need to be a biasagainst the walls of the vena cava to provide this quality.

DISCLOSURE OF INVENTION

According to the exemplary embodiments, there is provided, avessel-implantable filter of shape memory material with temperatureinduced austenitic and martensite states which may be easily removed bya single removal device after an extended period of time withoutsignificantly injuring the vessel wall. In the exemplary embodiments,the filter is of shape memory material which operates in a temperatureinduced austenitic state to exert a force on the wall of a vessel bymeans of oppositely disposed second extension elements to maintain thefilter in place, but which may easily be removed after the endotheliumlayer has covered the ends of the filter second extension elementswithout significant damage to the vessel wall.

Preferably, a group of first extension elements and a group of secondextension elements incline from a central axis. Preferably, also, theends of the first extension elements in the group of first extensionelements are oriented to engage a vessel wall to orient and center thefilter in the vessel, and the ends of the second extension elements ofthe group of second extension elements are oriented to engage the vesselwall to prevent longitudinal movement of the filter along the vessel.More preferably, the ends of at least some of the first extensionelements are also configured to engage the vessel wall. For example, theends of at least some of the second extension elements may be providedwith hooks configured to be more elastic than the second extensionelements to permit the hooks to straighten in response to a withdrawalforce to facilitate withdrawal from the endothelium layer without riskof significant injury to the vessel wall. In preferred embodiments,somewhat different engagement elements can be formed on the ends of atleast some of the first extension elements as described below.

Preferably, the hooks are elastic and formed on the free end of anappendage to pierce the vessel wall and insure that the filter remainsstable even in response to movement, such as respiratory functions or inthe event of a massive pulmonary embolism. The hook is formed to have amaximum migration force, and when subjected to forces below the maximummigration force, the hook retains its shape. When subjected to forcesabove the maximum migration force, the hook straightens and canautomatically disengage without significant damage to the vessel wall.

In a further embodiment, there is provided a vessel implantable filterwith a plurality of expandable appendages extending radially away from acentral axis such as to contact a cylindrical channel in which thefilter is inserted, which contact points are displaced bothcircumferentially around the axis and axially along the axis. Also, theappendages are urged outwardly by some means, such as by a resilience ofthe material of which they are made combined with the particularconfiguration. As a result of the axial displacement of some contactpoints relative to other contact points, the filter axis aligns with thechannel axis. As a result of the radial displacement of the contactpoints, the filter axis is centered.

In the foregoing embodiment, at least two of the appendages, whoserespective contact points are displaced axially relative to one another,have tips that are designed to engage the wall of a vena cava due to theurging thereof. Preferably, this engagement is by way of a sharp tipthat penetrates the vena cava wall. Preferably the tip is provided witha stop to prevent more than a predetermined amount of penetration. Inthis case, preferably, the sharp tips are designed to be capable of onlylimited penetration force owing to a flexibility of the appendages whichcauses the appendages to yield, mechanically, when more than thepredetermined penetration force is applied. Alternatively, and/or inaddition, the tips or the appendages are formed such that when a forceis applied in the axial direction, the engaging tips (e.g., the sharptips) of the appendages flex when more than a predetermined amount offorce is applied. In the latter case, this is such as to permit thefilter to be withdrawn by applying more than the predetermined amount offorce.

In a preferred variation of the foregoing embodiment, the appendages arearrayed in two circular arrays which are offset or spaced along theaxial direction. In this case, the appendages at one end may be referredto as second extension elements and the appendages at the other end maybe referred to as first extension elements. More preferably, both thefirst extension elements and the second extension elements have featuresat their extreme ends which are designed to engage the wall of a venacava in such a way as to resist axial force. Preferably, the total forcethe appendages/tips can resist is no more than that required to resistblood flow pressure of 50 mm Hg over the cross-sectional area of thevessel. By providing some support from the first extension elements aswell as the second extension elements, the total force peraxial-load-resisting contact point is reduced. For example, if the tipsare sharp and penetrate the vessel wall, the load per vessel-wallpenetration is thereby reduced, causing reduced risk of trauma,particularly upon withdrawal of the filter.

According to another embodiment, a blood clot filter has a trap sized tofit into a blood vessel and configured to hold an embolus. The filterincludes wall-contacting members that define and resiliently extend fromthe trap. A first portion of the wall-contacting members have firstsurfaces that engage the vessel wall. A second portion of thewall-contacting members have second surfaces that engage the vesselwall. The first surfaces are constructed to engaging the wall in such amanner that the first portion of the wall-contacting elements resistdownstream movement due to blood flow even when an embolus is held inthe trap; the second surfaces engaging the wall in such a manner thatthe second portion of wall-contacting elements resist upstream movement.

Preferably, the second surfaces are more effective to prevent upstreammovement than to prevent downstream movement. Preferably, each of thesecond surfaces defines a sharp tip that is angled such that the tiptends to withdraw from the vessel wall if the second portion of thewall-contacting elements is moved in the downstream direction.Preferably, the second portion of the wall-contacting elements areconfigured to buckle, thereby changing the angles of the sharp tips suchthat the sharp tips tend to withdraw from the vessel wall on upstreammovement. Also, in a variant embodiment, the second portion of thewall-contacting elements are configured to buckle when the filter movesin an upstream direction. Also, in another variant embodiment, the wallcontacting surfaces of the first and second portion of thewall-contacting members are axially displaced relative to each other toserve to orient the filter in the blood vessel. In yet another a variantembodiment, the first portion of the wall-contacting members haverespective weakened portions that are shaped to limit the amount ofradial force the first surfaces apply to the vessel wall.

In the previous embodiment, each of the second surfaces can define asharp tip and the second portion of the wall-contacting members caninclude straight and bent portions or be continuously curved. Theoutward bends present radially-outward surfaces that contact the vesselwall in such a manner as to limit the penetration depth of therespective sharp tips. Preferably, in the latter variant, the secondportion of the wall-contacting members are formed by wire extensions andthe bent or curved structures have bends at the ends of the wireextensions. In yet another a variant embodiment, the wall-contactingmembers are configured to fold into a cylindrical package for insertioninto and removal from a blood vessel.

According to an embodiment, a blood clot filter has leading and trailingends and a longitudinal axis. The trap is collapsible toward thelongitudinal axis for insertion into a blood vessel and radiallyexpandable outwardly from the longitudinal axis to an expandedconfiguration to contact and penetrate an inner wall of the blood vesselto provide a downstream migration resisting force. A plurality ofelongate, spaced appendages preferably have ends which are centrallyinterconnected at the longitudinal axis and further have remote endsextending radially away from the longitudinal axis in the expandedconfiguration of the trap. A first portion of the elongate spacedappendages have pointed hooks formed at the second ends thereof pointingaway from the longitudinal axis to engage and penetrate the vessel innerwall in the expanded configuration. Each hook is formed with a maximummigration force such that a force above the maximum migration forceapplied to the hook as a result of a withdrawal force in excess of thefilter migration resisting force applied to the trailing end of thefilter in a direction away from the filter leading end will cause thehook to straighten. A second portion of the elongate spaced appendageshave multiple protruding portions that indent and protract the vesselinner wall when urged into contact therewith.

In a variant of the above embodiment, the second portion of appendagesare repeatedly bent in the radial direction to form undulations thatdefine the multiple protruding portions. In another variant of the aboveembodiment, the second portion are repeatedly bent in thecircumferential direction to form undulations that define the multipleprotruding portions. In another variant, the ends of the second portionof appendages are downstream of the ends of the first portion ofappendages. In another variant, the first and second portions of theelongate spaced appendages define respective upstream and downstreamcorollas. In yet another variant of the previous embodiments, the secondportions are repeatedly bent in the radial direction to form undulationsthat define the multiple protruding portions. In yet another variant,the second portion is repeatedly bent in the circumferential directionto form undulations that define the multiple protruding portions. Theends of the second portion of appendages are preferably downstream ofthe ends of the first portion of appendages.

According to an embodiment, a blood clot filter has a trap havingleading and trailing ends and a longitudinal axis, the trap beingcollapsible toward the longitudinal axis for insertion into a bloodvessel and radially expandable outwardly from the longitudinal axis toan expanded configuration to contact and penetrate an inner wall of theblood vessel to provide a downstream migration resisting force. Aplurality of elongate, spaced appendages having ends preferablycentrally interconnected at the longitudinal axis and further includingremote ends extending radially away from the longitudinal axis in theexpanded configuration of the trap. A first portion of the elongatespaced appendages have pointed hooks formed at the second ends thereofpointing away from the longitudinal axis to engage and penetrate thevessel inner wall in the expanded configuration. Each hook is formedwith a maximum migration force such that a force above the maximummigration force applied to the hook as a result of a withdrawal force inexcess of the filter migration resisting force applied to the trailingend of the filter in a direction away from the filter leading end willcause the hook to straighten. A second portion of the elongate spacedappendages have sharp tips with stops that limit the depth to which thesharp tips can penetrate the vessel inner wall.

In a variant of the foregoing embodiment, the second portion ofappendages are bent to define the stops. Moreover, the sharp tips of thesecond portion are preferably aimed in an upstream direction when thefilter is expanded and emplaced in the vessel. The sharp tips may beconfigured such that a downstream movement of the filter causes thesharp tips to withdraw from the vessel inner wall. The ends of thesecond portion of appendages are preferably downstream of the ends ofthe first portion. The first and second portions of the elongate spacedappendages preferably define respective upstream and downstreamcorollas. In an embodiment, the ends of the second portion of appendagesare downstream of the ends of the first portion. The first and secondportions of the elongate spaced appendages may define respectiveupstream and downstream corollas.

According to an embodiment, a blood clot filter has a hub extending in ahub direction from a first hub end to a second hub end along alongitudinal axis. A plurality of second extension elements extend awayfrom the second hub end along the longitudinal axis, each of the secondextension elements having a second extension element end proximate thehub and a hook at or near a distal end of the second extension elementto retain the second extension element to a blood vessel wall. Aplurality of first extension elements extend away from the second hubend along the longitudinal axis. Each of the first extension elementshas a first end and free end, the first end of each first extensionelement preferably being contiguous with a portion of the secondextension element. In addition, the free end of each first extensionelement is preferably closer to the axis of the filter than the hook ofeach second extension element. Moreover, the free ends of each of thefirst extension elements are preferably spaced equiradially from thelongitudinal axis. At least some of the first extension element freeends have features to engage the vessel inner wall to promote stabilityof the filter.

In a variant embodiment, at least some of the first extension elementfree ends have features more effective to prevent upstream movement thanto prevent downstream movement. In a further variant, each of the atleast some of the first extension element free ends having featuresdefines a sharp tip that is angled such that the tip tends to withdrawfrom the vessel wall if the second portion of the wall-contactingelements is moved in the downstream direction. In yet another variantembodiment, the first extension elements are configured to buckle,thereby changing the angles of the sharp tips such that the sharp tipstend to withdraw from the vessel wall on upstream movement. In theprevious embodiment, the first extension elements can be configured tobuckle when the filter moves in an upstream direction. The firstextension elements may be axially displaced relative to the secondextension elements to serve to orient the filter in the blood vessel. Inthis case, preferably, the first extension elements have respectiveweakened portions that are shaped to limit the amount of radial forcethe first surfaces apply to the vessel wall.

According to an embodiment, a blood clot filter has a hub extending inan axial direction with radially extending elements having vesselwall-engaging ends. First radially extending elements have firstwall-engaging ends configured to engage a vessel interior wall andthereby prevent downstream movement of the filter. Second radiallyextending elements having second wall-engaging ends configured to engagea vessel interior wall and thereby prevent upstream movement of thefilter. The second radially extending elements are preferably configuredto bend more easily in a first direction than a second.

In a variant of the foregoing embodiment, the second radially extendingelements preferably have a U-shaped or channeled cross-section, with theinterior of the U-shape facing away from the axis of the filter. Inanother variant, the second radially extending elements are repeatedlybent in the radial direction to form undulations that define multipleprotruding portions. Alternatively, the second radially extendingelements may be repeatedly bent in the circumferential direction to formundulations that define multiple protruding portions. In a particularembodiment, the ends of the second radially extending elements aredownstream of the ends of the first. In the foregoing embodiment, thefirst and second radially extending elements define respective upstreamand downstream corollas.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and constitutepart of this specification, illustrate exemplary embodiments of theinvention, and, together with the general description given above andthe detailed description given below, serve to explain the features ofthe invention.

FIG. 1 is an isometric view of a vena cava filter of the prior art.

FIG. 2 is an isometric view of the filter of FIG. 1 positioned in a venacava.

FIG. 3A is an isometric view of a filter according to an embodiment ofthe invention.

FIG. 3B illustrates an alternative extension element that has a surfacewith protrusions and recesses.

FIGS. 4A and 4B illustrate a detail of an first extension element of thefilter of FIG. 3A in a narrow and wide channel, respectively.

FIGS. 5A-5D illustrate various alternative configurations for providinga feature that protracts and indents the vena cava wall to providetractive resistance to migration.

FIG. 6 is an isometric view of a filter according to another embodimentof the invention.

FIGS. 7A and 7B illustrate a detail of an first extension element of thefilter of FIG. 6 in a narrow and wide channel, respectively.

FIG. 8 is a detailed end view that can be incorporated in any of theextension elements of FIGS. 3A-6.

FIGS. 9A and 9B show an first extension element of a further embodimentof the invention, FIG. 9A in cross section and 9B from the side.

FIG. 9C shows the embodiment of a FIG. 9A in an axial direction as itbends in response to a force aligned in a caudal direction.

FIGS. 10A through 10C show an extension element that permits force to beapplied in a radial direction, but which buckles when too much force isapplied in a caudal direction with FIGS. 10A and 10B showing theextension in cross-section and FIG. 10C showing the extension in planview.

FIGS. 11-14 show a filter design whose first extension elements bucklewhen a force is applied in a caudal direction but which are capable ofsupporting a radial force.

MODE(S) OF CARRYING OUT THE INVENTION

Referring to FIGS. 1 and 2, the filter 100 is shown in an expandedstate. Preferably, the filter is made of metal wires held together by ahub where they are joined, for example, by plasma welding. The wires arepreferably made of shape memory alloy with a martensite phase thatallows the wires to be straightened so as to enable insertion in acatheter and deployment therefrom. In the austenitic phase, the filterrecovers to its expanded state, which is illustrated.

The filter 100 has a double basket or trap design with first extensionelements 105 forming one basket or trap and second extension elements110 forming a second basket or trap. Each of the extension elements 105,110 have one end substantially centrally interconnected at thelongitudinal axis of the filter 100 and a remote or distal end thatextends radially away from the longitudinal axis. Alternatively or inaddition to, where the centrally interconnected ends of the extensionselements 105, 110 are axially spaced along the filter axis (not shown)the filter can present axially spaced corollas, one upstream and onedownstream. Both the first extension elements 105 and second extensionelements 110 engage the walls of the vena cava 107 after deployment. Thesecond extension elements contain hooked ends 115 that penetrate thevena cave 107 wall and prevent the filter 100 from moving downstream dueto the frictional force of blood moving past it. Preferably, the hookedends 115 are configured to yield upon the application of a specifiedamount of force to ameliorate retrieval.

Referring to FIG. 3A, a vena cava filter has first extensions 305 thathave multi-protrusion surface part 307 and second extensions 310 withengagement elements 330. In the example shown, the multi-protrusionsurface part 307 is a wire that undulates in a radial direction towardand away from a radial center aligned with the filter axis, which mayfurther define the axis of blood flow as indicated by the arrow 301. Themulti-protrusion surface part 307 may take other forms. For example themulti-protrusion surface part 307 could also include an engagementelement 330, as shown for example in FIG. 3B, with a portion 332 nearthe end 334 that undulates preferably in the circumferential directionabout the filter axis. The particular shape of the undulations depictedin the embodiment of FIG. 3B may vary. For example, they may not be 90°and 180° bends but could be greater than or less than these such as todefine diagonal traverses in the circumferential direction. In addition,in any of the embodiments described thus far, the wires need not havecircular cross-sections, but could have ellipsoidal, oval, rectangular,or other cross-sectional shapes and could also be hollow orintermittently hollow. In addition, the wires could be compositestructures with a skin of one material and a core, which could also behollow, of another material. By “composite” the inventor does not intendto limit the embodiments to structures with fixed elements, such asfibers in a polymer matrix. Rather composite structures could havemultiple movable or non-movable elements. Some particular examples ofdifferent structures are disclosed below in connection with specificfunctional enhancements. Both of these configurations 300 and 330 createindenting portions 336 and gaps or recesses between them that causetissue to protract as discussed with reference to FIGS. 4A and 4B,below.

Referring to FIG. 4A, the multi-protrusion surface part 307 when pressedagainst the vena cava wall 315 by the urging force of the attached firstextensions 305, protracts the tissue of the wall slightly as indicatedat 312. This tissue protraction and indentation resists the tendency ofthe first extension element to “ski” along the wall thereby resistingany migration. Migration in the cranial direction may be resisted byengagement elements 330 that penetrate, such as for example, hooks 330that withstand the force of flowing blood. However, it may be desirableto achieve greater stability, without interfering with the function ofthe filter or health of the patient. The feature 307 in the firstextensions 305 resists such movement and also helps to resist movementin the cranial direction by the same mechanism. By assisting in theresistance of movement in the cranial direction, the feature 307 mayreduce the load on tissue resulting from the penetration of the hooks330 on the second extensions 310. As a result, the risk of trauma causedby cranial force on the tissue engaged with the penetrating elementssuch as hooks 330 may be reduced. To exploit this advantage, the yieldthreshold of the hooks 330 may be lowered. Note that other penetratingelements may be employed such as disclosed in the prior art, forexample, barbs, edged shoes (e.g., as described in U.S. Pat. No.5,755,790), or roughened surfaces.

Note that not all of the second extensions 310 need have hooks 330provided on them. For example, barbs or roughened surfaces that permittissue growth over them could be used. However, it is preferred to use afeature that is immediately effective such as a barb, hook, or shoeswith edges, since the device may need to resist the forces of thecranial flow immediately after implantation.

The multi-protrusion surface feature 307 provided on the first extensionelements 305, as seen for example in FIG. 3A, can alternatively beimplemented on some of the second extension elements 310, or further inthe alternative, in a combination of the second extension elements 310and first extension elements 305. Preferably, a first extension elements310 with the multi-protrusion surface feature 307 would not have hooks.Referring particularly to FIGS. 4A and 4B, the multi-protrusion surfacefeature 307 of the first extension elements 310 are curved so that whenthe filter 300 is narrowly confined, a middle or upper portion 303 ofthe multi-protrusion surface feature 307 presses against the vena cavawall 315 and when the filter 300 is in a wider channel, a region 304closer to the end 325 presses against the vena cava wall 315. Thediscussion of this paragraph applies to the extension 330 of FIG. 3B aswell.

Although six first extension elements 305 and six second extensionelements 310 are illustrated, there can be a different number. Forexample, preferably the number is at least three of each, and morepreferably, there may be four to twelve first extension elements 305and/or four to twelve second extension elements 310. The first extensionelements 305 and second extension elements 310 may be symmetricallyarrayed about the hub 302 or asymmetrically arrayed thereabout, howeverthis is not essential. Since the materials are very resilient, theoverall shape will conform with the anatomy of the patient beingtreated. Also, varying the lengths of the first 305 and second 310extension elements may be useful for most particular embodiments if theend features, such as hooks, are prone to interfere with each other whenthe device is packed in a catheter for delivery. However, the materialof which the extension elements are made may be a shape-memory materialthat allows the hook and undulating parts to assume a straightconfiguration that ameliorates packaging.

Although hooks 330 are an extension element feature that can preventdownstream movement within a vessel, i.e. in the cranial direction ofthe filter, other engagement features can be employed. For example, theextension elements may include one or more barbs located at or neartheir ends in order to engage the vena cava wall. Such an engagementfeature need not need not necessarily taper, as is the case with a hookthat preferably tapers to a point. Instead, it may be sufficient for aconstant diameter portion of the engagement element to have a bend whichturns toward the wall of the vena cava. Further in the alternative,tractive resistance may be supplied with no end hooks or barbs if theradial forces in the extension elements are sufficient to provide theneeded resistance. Note further that the extension elements need notcollectively taper to form the trap as seen, for example, in FIG. 3A.For example, it would be sufficient for the extension elements to servethe function of assisting in orienting the filter if there are contactpoints that are relatively displaced in the flow direction.

Although in the embodiment of FIG. 3A, the first extension elements 305are the portions of the filter 300 whose contact portions (e.g., 303,304 in FIGS. 4A and 4B) are at the cranial-most end of filter 300, themulti-protrusion surface parts 307 can be located such that themulti-protrusion surface parts 307 are at the caudal end of the filteror both the caudal an cranial ends of the filter as well, as seen forexample, in FIG. 5A. Also, the supporting features of the filter do notneed to be extending first extension elements as in the embodiment 300.They can assume other shapes that provide the functions of the orientingand engaging function of the multi-protrusion surface part 307. Also, acomplementary component that engages the vena cava wall need not beprovided on extensions that stem from a hub like branches of a tree. Thefilter 339 of FIG. 5A illustrates such alternatives. In the filter 339,a flexible hoop 340 has hooks 353 attached thereto which engage the venacava wall. Preferably, the hoop 34 is flexible so as to allowconformance with a range of vena cava sizes. The flexibility may beaugmented by providing relief portions 354 of an alternative hoop 352structure as shown in FIG. 5B. Multi-protrusion surface parts 364 areprovided on extensions 345. The hoop 340 is joined to the extensions 345by a hub 350 located near the axial middle of the filter 339. Morespecifically, the hub 350 is preferably an elongate tubular memberhaving a first hub end and a second hub end axially spaced from thefirst hub end along the axis of the filter 339. The first hub end ispreferably joined to the hoop 340 and the second hub end is preferablyjoined to the extensions 345 to couple the extensions 345 to the hoop340. Due to their relative orientation, the extensions 345 and the hoop340 can provide upstream and downstream corollas.

Note that in the filter 339, the movement resisting hooks 353 arepositioned to make contact with the vena cava at cranial-most contactpoints while the multi-protrusion surface parts 364 are located to makethe caudal-most contact points of the filter 339. Also, the extensions345 that define the multi-protrusion surface parts need not be openended structures, for example, as shown in FIG. 5C, a loop 362 canpresent the contact feature such as the multi-protrusion surface parts363 or other contact structure sufficient to provide the desiredtractive resistance. Finally, the filter need not be configured suchthat the types of contact features, whether soft-engaging, i.e.,tractive resistant or frictional, such as multi-protrusion surface partsor hard-engaging, i.e. penetrating, such as hooks, are located atopposing ends of the filter. For example, as shown in FIG. 5D, hooks 373and multi-protrusion surface parts 374 can be co-located at both ends(or alternatively, one end, which is not depicted). Also, there need notbe a separate hub or other elements to tie the extensions 372 and 374together. For example, as shown, a tangle 376 of the extensions 372 and374 may serve that function.

Referring now to FIG. 6, in another exemplary embodiment of a filter400, first extension elements 405 and second extension elements 410preferably carry respective engagement elements 415 and 430 which arepreferably configured as hooks as shown. In this case, the shapes of thefirst extension element hooks 415, which resist any force in the caudalor upstream direction, are shaped to limit the penetration depth asshown in FIGS. 7 and 8. Also, the hooks 415 are shaped to serve thecaudal force-resisting function. Accordingly, as shown in FIG. 8, thehooks 415 are shaped such that they project into the vena cava 440 walland define an angle co therewith so that upon any cranial movement, theytend not to dig further in or alternatively configured to withdraw.Thus, the extreme tips 434 of the hooks 415 are angled slightly towardthe caudal direction such that he angle 0) is preferably made acute. Tolimit the penetration depth of the tips 434, a stop may be provided. Thestop is preferably formed by a tight radius bend defining an acuteundulation or knee-shaped structure 433 adjacent the hook 415. Thesurface of the knee shaped structure 433, upon contact with the venacava wall 456, stops or limits the tip 440 from penetrating deeply intothe wall 456. Alternatives such as a bulge or plate at the end of theextension element may also be used as a stop provided it acts to limitthe penetration of the tip 440 into the wall 456.

The feature of FIG. 8 may be used in place of the any of theaforementioned multi-protrusion surface features. The radial forceapplied to the hook 434 feature may be limited by providing a weakbuckling portion 425, with a flattened or smaller cross-sectional areathan the rest of the extension element. The buckling portion 425preferably bends radially outward as shown in FIG. 7B when more than apredetermined amount of radial (and axial) force is applied urging thetip 415 into the vena cava wall.

A limit on the amount of force that must be withstood by the vena cavacan be imposed by suitably configuring the extension element 405, 410.For example, the extension element 410 can be shaped so as to preferablybuckle when a threshold exceeding caudal force (schematically indicatedby arrow 493 in FIG. 9C) is applied to it. Accordingly, the extensionelement would be configured to apply a limited radial force to the venacava wall, and moreover would be limited in the penetrating force withwhich the tip can be urged into the vena cava wall 440. On exemplaryshape for buckling is shown in FIG. 9A. The cross-sectional shape of anextension element 490 can have a large aspect ratio, such as anelliptical portion 494 extends a substantially linear portion 497 of theextension 490. If the long axis of the ellipse is aligned with theradial direction, the extension 490 can apply a significant radialforce. But if a caudal force is applied to the filter a major componentof the force will be along the length of the thin extension 490 in theaxial direction which is suitable to cause the extension 490 to buckleas shown in FIG. 9B in which the extension 490 is shown looking from thecranial end of the filter in an axial direction toward the caudaldirection where the tip 415 terminates the extension 492.

FIGS. 10A to 10C illustrate an alternative mechanism for limiting thecaudal force that can be transmitted through a filter extension 530 tothe tip 535 of the extension 530. In this embodiment, the cross-sectionresists bending in one direction as illustrated by arrow 516 but isrelatively easy to bend in the other direction as illustrated by arrow517. In the illustrated embodiment, the extension has a U-shapedcross-section extending along a portion 532 of the extension 530. Therecess 555 of the portion faces away from the axis of the filter. If acaudal force is applied, the extension 530 will bend as illustrated inFIG. 10C by the arrow 519. This rotates the tip 535 so that it is noturged further into the vena cava wall. Note that a V-shapedcross-section or any other channeled configuration may be used providedthat it is effective to limit the caudal force transmitted through thefilter extension 530 to the tip 535. Another alternative is illustratedin FIGS. 11 through 14 in which a portion 615 of the extensions 610 haveslots 621 in the extensions 610 that are located to define a thickbridge 616 and a thin bridge 620. As a result of this structure, whichmay be flat or round in cross-section, if a caudal force is appliedthrough the extension 610, the thin bridge 620 is forced to resist acompressive force along its length, which, because the thin bridge 620is thin, cannot be withstood beyond a threshold. Thus, the portion 615bends as shown in FIG. 14. As shown in FIG. 13, when a radially outward(toward the vena cava wall 640) force is applied through the extension610, the thin bridge 620 acts in tension and can sustain a substantialforce allowing the extension 610 to apply the radial force against thevena cava wall 640. The tip 630 may be as in the foregoing embodiments.

As discussed, while it is possible that the filter could be made fromductile metal alloys such as stainless steel, titanium, or elgiloy, itis preferable to make it from Nitinol. Nitinol is a low modulus materialwhich allows the extensions of the device to be designed to have lowcontact forces and pressures while still achieving sufficient anchoringstrength to resist migration of the device. The force required to causethe discussed buckling and yielding behavior can be adjusted to thetotal force required to resist filter migration in the respectivedirection. This can be accomplished by changing the cross sectional areaor geometry of the extensions, by material selection, or a combinationof these.

The force or stress which is required to deform the various deformableportions can be correlated to the force applied to such part under thethreshold load conditions. For example, this may correspond to normalhuman peak blood pressure multiplied by a maximally occluded conditionof the filter.

The preferred embodiment corresponds substantially to filter structuresin which first extension elements and second extension elements extendfrom a common hub. In that embodiment, the stabilization features may beprovided on the first extension elements. Thus, in the presentspecification where an embodiment of an extension is discussed withoutreference to a specific structure and the extension provides astabilization function, it is preferred that the feature be provided onthe first extension elements 105 of a device having a generalconfiguration as that of FIG. 1. In such an embodiment, the firstextension elements 105 aid in centering and provide a secondaryfiltering level. The first extension elements are preferably curved suchthat the ends of the first extension elements are bent inwardly. Thecurved parts minimize the possibility of the first extension elementengaging the vena cava wall or side branches and the length of the firstextension elements reduces the possibility of the first extensionelement being bent upward. The migration resisting features may beemployed on a single first extension element or any or all of the firstextension elements, preferably six in number.

Again, regarding the preferred general filter configuration, themulti-protrusion surface feature can be created by locally bending thewire at intervals along the length of the first extension element. Byadding the protrusions along the length of the first extension elementthey will provide resistance in a both small in large vena cavas. In theembodiments with tip hooks that resist caudal forces, the engagementforce is controlled by two mechanisms. First, the extension element hasa penetration depth stop which limits the penetration into the wall.Second, the extension element is designed to buckle or collapse at apredetermined load in order to limit the amount of penetration force.One or both of these design features can be used to control theengagement with the wall. The first extension element is preferablydesigned to center the filter by applying a sufficiently high radialforce component. The stabilization features may employ one or more firstextension elements.

While the present invention has been disclosed with reference to certainembodiments, numerous modifications, alterations, and changes to thedescribed embodiments are possible without departing from the sphere andscope of the present invention, as defined in the appended claims.Accordingly, it is intended that the present invention not be limited tothe described embodiments, but that it has the full scope defined by thelanguage of the following claims, and equivalents thereof.

1. A blood clot filter, comprising: a first set of members and a secondset of members defining a trap sized to fit into a blood vessel andconfigured to hold an embolus, each of the first and second membersbeing configured to resiliency extend from the trap; wherein at leastone of the first set of members includes a first surface for engagingthe vessel wall such that the at least one of the first set of membersresists downstream movement within the vessel, wherein further at leastone of the second set of members includes a second surface for engagingthe vessel wall such that the at least one second member resistsupstream movement within the vessel.
 2. The filter of claim 1, whereinthe second surface engages the vessel wall such that the at least onesecond member resists downstream movement, the second surface being moreeffective to prevent upstream movement than to prevent downstreammovement.
 3. The filter of claim 2, wherein the second surface defines asharp tip that upon penetration of the vessel wall defines an angle withthe wall such that the tip tends to withdraw from the vessel wall if thesecond set of member is moved in the downstream direction.
 4. The filterof claim 3, wherein the at least one of the second set of member isconfigured to buckle in response to a force acting on the at least onemember in the upstream direction such that the angle of the sharp tiprelative to the wall withdraws the tip from the vessel wall on upstreammovement.
 5. The filter of claim 2, wherein the second set of membersare configured to buckle when the filter moves in an upstream direction.6. The filter of claim 1, wherein the first surface and the secondsurface are axially displaced relative to each other to serve to orientthe filter in the blood vessel.
 7. The filter of claim 1, wherein the atleast one of the first members has a weakened portion shaped to limitthe amount of radial force applied by the first surface to the vesselwall.
 8. The filter of claim 7, wherein: the second surface defines asharp tip; and the at least one of the second set of members has aknee-shaped structure that presents a radially-outward surfaces to limitthe penetration depth of the respective sharp tip.
 9. The filter ofclaim 8, wherein the at least one of the second members is formed by awire extension and the knee-shape structure is defined by at least onebend at the ends of the wire extension.
 10. The filter of claim 1,wherein the first and second set of members are configured to fold intoa cylindrical package for insertion into and removal from a bloodvessel.
 11. A blood clot filter, comprising: a trap having leading andtrailing ends and a longitudinal axis, the trap being collapsible towardthe longitudinal axis for insertion into a blood vessel and radiallyexpandable outwardly from the longitudinal axis to an expandedconfiguration to contact and penetrate an inner wall of the blood vesselto provide a downstream migration resisting force; a plurality ofelongate, spaced appendages having ends centrally interconnected at thelongitudinal axis and remote ends extending radially away from thelongitudinal axis in the expanded configuration of the trap; a firstportion of the elongate spaced appendages having a hook directed awayfrom the longitudinal axis to engage and penetrate the vessel inner wallin the expanded configuration, each hook defining a maximum migrationforce such that a force above the maximum migration force applied to thehook in an opposing direction of the maximum migration force will causethe hook to straighten; and a second portion of the elongate spacedappendages having multiple protruding portions.
 12. The filter of claim11, wherein the second portion of appendages are repeatedly bent in theradial direction to form undulations that define the multiple protrudingportions.
 13. The filter of claim 11, wherein the second portion ofappendages are repeatedly bent in the circumferential direction to formundulations that define the multiple protruding portions.
 14. The filterof claim 11, wherein the centrally interconnected ends of the secondportion of appendages are downstream of the centrally interconnectedends of the first portion of appendages.
 15. The filter of claim 11,wherein the first and second portion of appendages define respectiveupstream and downstream corollas.
 16. The filter of claim 15, whereinthe second portion of appendages are repeatedly bent in the radialdirection to form undulations that define the multiple protrudingportions.
 17. The filter of claim 15, wherein the second portion ofappendages are repeatedly bent in the circumferential direction to formundulations that define the multiple protruding portions.
 18. The filterof claim 15, wherein the centrally interconnected ends of the secondportion of the appendages are downstream of the centrally interconnectedends of the first portion of the appendages.
 19. A blood clot filter,comprising: a trap having leading and trailing ends and a longitudinalaxis, the trap being collapsible toward the longitudinal axis forinsertion into a blood vessel and radially expandable outwardly from thelongitudinal axis to an expanded configuration to contact and penetratean inner wall of the blood vessel to provide a downstream migrationresisting force; a plurality of elongate, spaced appendages having endscentrally interconnected at the longitudinal axis and remote endsextending radially away from the longitudinal axis in the expandedconfiguration of the trap; a first portion of the elongate spacedappendages having a hook formed at the remote ends thereof pointing awayfrom the longitudinal axis to engage and penetrate the vessel inner wallin the expanded configuration, each hook being formed with a maximummigration force such that a force above the maximum migration forceapplied to the hook and in a direction opposing the maximum migrationforce will cause the hook to straighten; and a second portion of theappendages having tips to penetrate the vessel inner wall, the tipsincluding stops to limit the depth to which the tips can penetrate thevessel inner wall.
 20. The filter of claim 19, wherein the secondportion of the appendages are bent to define the stops. 21.-42.(canceled)